Electric discharge device seal



Aug 15 1950 w. J. scoTT 2,518,944

ELECTRIC DISCHARGE DEVICE SEAL Filed Feb. 2, t11.949

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Patented Aug. 15, 1950 ELECTRIC DISCHARGE DEVICE SEAL William Joseph Scott, Rugby, England, assignor to General Electric Company, a corporation of New York Application February 2, 1949, Serial No. 74,146 In Great Britain February 13, 1948 Claims.

This invention relates to electric discharge devices having an envelope of qu-artz or like vitreous material possessing a high refractive index, the envelope containing a discharge-supporting atmosphere which, during operation, is ionized and emits ultraviolet rays.

In order to achieve and maintain gas tightness of the envelope of such devices the seal(s) between the leading-in conductor(s) to the electrode s) and the wall of the envelope have to be carefully designed and constructed. The usual form of seal involves the use of a thin foil of molybdenum which, during the manufacture of the envelope, is embedded in a relatively thick rod-shaped stem of the vitreous material of which the envelope is composed, and which is joined to the wall of the envelope. It has been found that the electrical continuity and/or gastightness of such seals may deteriorate during the working life of the device, as a result of the action upon the sealed-in conductors of radiation transmitted from the interior of the envelope and along the stem containing the conductor seal, owing to the high refractive index of the vitreous material causing total. internal reflection within the stem. This transmission may result in the sealed-in conductor becoming unduly hot, and where it emerges into the air from the vitreous material and joins the usual terminal cap or base at the remote end of the stem oxidation may arise with accompanying deterioration of the conductor.

The principal object of the present invention is to provide means for averting the deterioration of the seal from this cause, and to this end the invention consists in constituting at least a portion of the vitreous material containing the sealed-in conductor of the device of a material which substantially reduces the transmission of radiation along the seal while not aiecting the gastightness of it.

This material may be silica, which. by the inclusion of a multiplicity of air bubbles therein, has been rendered opaque to such rays as ultraviolet and infrared and translucent to visible rays. A suitable material of this character is that known as Vitrosil A collar or disc of this material is accordingly arranged to constitute an integral part of the stem tube which contains the sealed-in conductor.

. In the accompanying drawing, species of the invention are shown in which Fig. 1 is an elevational, partly sectional view of a high pressure mercury vapor discharge lamp embodying the invention and Fig. 2 is a similar view of an electrically conducting stem embodying the invention and useful for the lamp shown in Fig. l.

Referring to Fig. l of the drawing, the lamp comprises a spherical envelope I of transparent quartz having two stems 2 and 3 protruding therefrom. The electrodes 4 and 5 in the envelope I are supported by bent metal rods 6 and I emerging from the stems 2 and I3, respectively. The larger electrode 4 is the anode and the smaller electrode 5, which is constituted by the inner end oi rod 1, is the cathode of the lamp. The rods E and 'I and anode 4 are of tungsten. The envelope I contains a starting gas, such as argon, at a few mm. pressure and a quantity of mercury, indicated by the droplet 8, the vapor of which is luminosity producing during operation oi the lamp. Lamps of this type are well known and are operated with a power input such that the mercury vapor pressure is of the order of many atmospheres.

The stems 2 and 3 are of similar structure and stem 2 is shown partly in section in Fig. l of the drawing to illustrate the structure of the stems. As shown, the stem 2 comprises a tube 9, also of transparent quartz, in which is embedded an electrical conductor including the tungsten rod 6 supporting the electrode 4 and a plurality of molybdenum foil strips I0 which are electrically connected to the inner end of rod 6 by tungsten wires II welded to the inner ends of strips I0 and to the end of rod 6. Similar wires I2 are welded to the opposite ends of the strips I0 and extend beyond the end of the stem tube 9 for connection to a base (not shown). The portion of rod 6 in tube 9 is wrapped with molybdenum foil I3 to prevent quartz adhering thereto during fabrication of the stem. The joint between rod E and tube 9 is thus a mechanical one. The hermetic joint between the quartz tube 9 and the conductor is at the strips IU onto which the hot quartz is collapsed during fabrication of the stem to make a gas-tight joint. The stems 2 and 3 usually comprise four or more strips I0 and are capable of carrying a heavy current to the electrodes 4 and 5.

Such stems are known and further description thereof and their method of manufacture are unnecessary for a complete understanding of my invention by those skilled in the art.

A disadvantage of stems of this type, as Well as with other types of stems, including that shown in Fig. 2 and described below, is in the tendency of the exposed parts of the conductor, that is the tungsten wires I2 and the ends o1' strips I 0 joined thereto, to oxidze at the elevated 3 temperatures to which they are subjected during operation of the lamp. The oxide coating creeps into the hermetic joints between the strips I and the quartz and the joints become gas pervious. Of course, the stems 2 and 3 can be made long enough so that the exposed portions of the conductor are; below the oxidizing temperature thereof during operation of the lamp but this expedient increases the cost of the lamp by requiring more material and complicates its ship 910 ping and mounting due to its larger size. In accordance with my invention, ultraviolet and infrared rays generated in'envelope handftravelling within the quartz tube 9 duringfope'ration-othe lamp are absorbed by an integral coll-ar I4 of quartz containing air bubbles.k y The stemszthus; may be made considerably shorten-without strips;r

l0 becoming oxidized to the extent that thejoints thereof with the quartz become gas pervious for a long useful operating "life of the lamp.

.The collar M'is made integralwiththe stem by heating an annular portion of the quartz tube with a .gas name tozvaporize away the quartz'of thisvztube portion. The heating is continued untilLan-.annular groove is formed'in the tube 9; A rod` of quartz 'containing' air bubbles is then heated-toits softening temperaturel and wrapped around the quartz tube Sto nl] upthe groove and form.` an integral part ofthe stem. l

TheV Stem shown'vin Fig. 2. of the drawing is useful fortheV lampsliown in Fig. 1 and come prises ametal conductor including a tungsten rod li'wrappedwith Vmolybdenum foil' IB'fand a molyb'denum disc Il hermetically united aroundthe rodl'5f-by'abrazedherrnetic joint E81 The disc Il tapers to a feathered sealing edge portion which is hermetcally embedded in the transparent quartzstem tube l9`. A disc or short tube 20er quartz y containing air bubbles isincorporated yin the stem tube I9 and the stem'is'fmounted on a lamp envelope with the discf1 ymore remote from the envelope than the quartz disc 2i). The quartz disc 20,1Iike the collar I4 of Fig. 1-,` absorbs'infrared` and* ultraviolet radiations" generated within thequartz-envelope of a lamp and traveling in the stem tube i9.- This reduces the temperature of the disc llv and the tendency ofthe Surface of the disc I1 facingaway'` from the quartz disc'KZG and: exposed tothe outside-atmosphere to o'xidi'ze'.Y r'Iheijoint between the thin'fmolybdenunr disc l1 and thefquartz tube I9 thus remains-gas-tightfor aelong useful life of thelamp;

Thefqu'artzldisc 20' may ber joinedto the transparent quartz parts of thetube lBFby butting the'- endsiof! transparent quartz tubes against the ends of the translucent 4quartz disc 20 and heating the jointslwith a gas name to thesoftening tempera-y ture ofif quartz toV hermeticallyfuseV the quartz members together. 'The` conductor' is then mounted? inandfjoined to-1the quartz part of the stem by heating the quartz to itssoftening'temperature and collapsing it onto the conductor' withi which -it makesv a mechanical joint except' atthefeatheredsealing edge ofj disc I7 whereith'e joint is hermetic. Stems of this type-are-disr closedv in yco pending application Seriali No.746',916, died-August' 303 1948l and assignedt'o tlfie'assigneev of:` the presentapplication.-

` What I claimasv-new and'des-ire'tosecure by Letters Patent ofA the United Statesisl:

i 1-. electric discharge'devioe-designectfor op,-VY eration lat elevated temperatures and comprising; anenvelope'fof material having ah-iglr refractive index;- an =ionizablej gaseous atmospherel in said' envelope capablegof-f-emitting electro=zn' rgneti'cra"a1 diations when excited by an electric discharge and a stem protruding from said envelope comprising a conductor which oxidizes at elevated temperatures and a tube of the envelope material hermetically united around said conductor with a portion of the conductor exposed to the outside atni'sphere, anannula'r p'oitii ors'aid tube between sa-id'entelope and the prtion thereof hermetically united with said conductor containing 'air bubbles to minimize the oxidation of the exposed,l portion of said conductor.

2. An electric discharge device designed for operational; elevated temperatures and comprising'ar quartz envelope, an ionizable gaseous atmosphere in said envelope capable of emitting e1ectro=magnetic radiations when excited by an electric discharge and a stem protruding from said envelope comprising a conductor which oxidizesv at elevated temperatures and a quartz tube hermetically united around said conductor with a prtion-of the conductor exposed to' the' outside atmosphere, an annular. portion of said tube be: tween said envelope and the portion .thereof her"-` nietieally united with said'conductorA including quartz containing air bubbles t substantially reS duce the transmission o radiation alonglthef stem andthereby minimize the oxidation ofthe exposediportion :of saidiconductor.

3; An electric discharge device. 'clesignedifor op; eration at elevated temperatures .and comprising av quartzfenvelope,v an ionizable gaseous* atmos;

pliere in said envelope capable` o'fiemitting elec` troemagn'etic radiations when excited byanielec.: tric.. discharge; and: a stem protruding from; said V'envc'elcipe.comprising a cc'mductorv which oxidizes at elevated'temperatures and ai quartz;tubel'ier metically unitedaround said conductor: with a portionxof: thepconductor exposed. to the outside atinos'phereiv av collarof quartz containing. air bubbles recessed into thewall of said'tube' be# tweensaidgenvelope'andV thef portion thereof: hermetically united with said'conductor to substam tia-ily vreducethe transmission fof radiation along thestem'zand thereby minimize the voxidation of therexposed portion of 'saidconducto'ri 4: Anelectrio discharge device designed forop erationat` elevated temperatures andcomprising aqu-artzrenvelope, an ionizable gaseous `atmospherefinvsa-id envelope capable of emitting-close troemag-netic radiations when excited by an electriccdischarge and a-stem protruding from said envelope comprising a conductor which oxidizes at eleva-ted temperatures and. ya. quartz. tube hermeticaily united aroundsaid conductor with a portion-.of the conductor lexposed` to4 the outside atmosphere! an annularqsection `of saidtube wall between-said envelopefnand` the portion thereof` hermeticallyunited with: saidconductor v being of quartzpontaining air bubbles to substantially reduce the. transmission of radiation along the stem and thereby minimize the oxidation of the ex posed-portionof saidconductor.

5., n electrically conducting stem for aliigh temperatur'egdevice, comprising an electrical. conductor whichoxidizes at elevated temperatures) andla silica tbel'ermetic'ally united around. a portion .of-.said conductor with. an end prtion of tlie.. conductor exposed at-the. outer endV f the. tul'i'e',k an annularprtin of said silicatubec'oiitaining air bubbles to substantiallylduce, the transmission of radiation al'n'g the stein and tlereby.4 minimize'. thev oxidation of `tl`1`e exposed Pfitinoisaid nductfr". I p

WILLIAM JOSEPH. SCOTTI REFERENCES CITED UNITED STATES PATENTS Number Name Date 1,558,524 Winninghoff Oct. 27, 1925 2,020,724 Fritze et al NOV. 12, 1935 Number Number Name Date Hagen et al Nov. 8, 1938 Brandt Mar. 12, 1940 FOREIGN PATENTS Country ,D ate Great Britain Feb. 8, 1943 Australia May 1, 1942 Australia. July 1, 1943 

